How to maintain the boiler interior after it is shut down?

There are several methods for maintaining a boiler when it is taken out of service: 1. Pressure maintenance – This method can be used when the boiler will not be out of service for more than a week. That is, before the shutdown process is completed, the steam-water system should be filled with water, the residual pressure should be maintained at (0.05~0.1) MPa, and the temperature of the boiler water should be kept above 100°C; this will prevent air from entering the boiler. The measures to maintain the pressure inside the boiler at a certain temperature are: heating with steam from an adjacent boiler, or regular heating of the boiler itself. 2. Wet maintenance: When the boiler is out of use for no more than a month, wet maintenance can be employed. Wet maintenance involves filling the boiler’s steam and water system with soft water containing alkali solution, leaving no air space. This is because an aqueous solution with the appropriate alkalinity can form a stable oxide film on the metal surface, thereby preventing further corrosion. During wet maintenance, the furnace should be dried regularly using a low heat to keep the outside of the heated surfaces dry. The pump should be operated regularly to ensure the water circulates. Regularly test the alkalinity of the water; if it decreases, an appropriate amount of alkali should be added. 3. Dry maintenance: When the boiler is not in use for an extended period, dry maintenance can be employed. Dry maintenance refers to the method of using desiccants inside the boiler and furnace for protection. The specific procedure is as follows: after shutting down the boiler, drain all the water from it; use the remaining heat in the furnace to dry the boiler, remove any scale or debris inside it promptly, then place trays containing desiccants inside the boiler drum and on the grate. Finally, close all valves as well as any access doors and manholes. Regularly check the maintenance status and replace the expired desiccant in a timely manner. 4. Inflation maintenance: Inflation maintenance can be used for long-term shutdown maintenance of the furnace. After the boiler is shut down, do not drain the water; keep the water level at a high level. Take measures to deoxidize the boiler water, and then isolate it from the outside environment. Nitrogen or ammonia is introduced to maintain the pressure after inflation at (0.2~0.3) MPa. Since nitrogen can react with oxygen to form nitric oxide, this prevents oxygen from coming into contact with the steel plate. Ammonia makes water alkaline when it dissolves in it, which effectively prevents oxygen corrosion; therefore, both nitrogen and ammonia are excellent preservatives. Inflation maintenance yields good results; to achieve this, the boiler’s steam and water system must have good tightness. During the shutdown process of the boiler, a series of maintenance tasks must be carried out to prevent the boiler water from causing corrosion to the boiler. Compared to ordinary boilers, vacuum boilers are much easier to maintain. This is because the heat transfer water in the vacuum boiler is specially treated, and it is completely sealed, thus not coming into contact with external air. So there is no need to worry about corrosion occurring inside the boiler after it is shut down

It’s not called inflation maintenance; it’s called nitrogen filling maintenance. Nitrogen can be used for about a month, but the pressure needs to be checked regularly – if it drops, more nitrogen needs to be added. It’s still quite a hassle

Are there any relevant standards available?

There are no relevant standards for this, but maintenance methods are mentioned in some related materials; operating procedures also usually include information on this. If needed, add me on WeChat and I’ll send you a nitrogen filling maintenance plan

Safety indicators for boiler operation: The safety indicators for boiler operation cannot be measured directly; instead, they are assessed using the following indirect indicators. 1. Hours of continuous operation of the boiler: The hours of continuous operation of a boiler refer to the number of hours it operates between two instances when it has to be shut down for maintenance. 2. Boiler availability The boiler’s availability refers to the sum of the total operating hours and the total standby hours of the boiler during the statistical period. The percentage of the total hours in that statistical period, that is, the availability rate of the boiler. 3. Boiler accident rate: The boiler accident rate refers to the percentage of the total hours the boiler was shut down due to accidents, expressed as a ratio of the total number of hours the boiler was shut down due to accidents to the total number of hours it was in operation during the statistical period. The statistical period for calculating both the availability rate and the accident rate can be one year or two years; the longer the continuous operating time, the lower the accident rate, and the higher the availability and utilization rates. The higher the safety and reliability of the boiler, the better. At present, the continuous operation hours of large and medium-sized power plant boilers in our country exceed 5,000 hours, with an accident rate of about 1% and an average availability of around 90%.

There is a “Boiler Operator’s Handbook” on the forum; it is recommended to download it for study*